This revision application to 5R01 GM084724-06 has been submitted in response to Notice Number NOT-OD-09-058, entitled "NIH Announces the Availability of Recovery Act Funds for Competitive Revision Applications." The application represents a significant expansion of the scope of the original project to investigate the role of O-GlcNAc (O-linked N-acetyglucosamine) glycosylation in learning and memory. Developing an understanding of the molecular mechanisms that underlie learning and memory stands as one of the central challenges of modern science. Our proposed studies will focus on a carbohydrate modification that plays a central role in this process: O-GlcNAc glycosylation. O-GlcNAc glycosylation is a dynamic, intracellular modification found on proteins involved in gene expression, cell signaling, and synaptic plasticity. A major goal of our work is to develop an understanding of the molecular mechanisms by which this sugar influences neuronal communication and information storage. Long-term memory is widely believed to occur through changes in synapse number and strength during learning. Such changes, termed "synaptic remodeling," require new protein synthesis in dendrites, the branched projections on the cell that conduct nerve impulses from the synapse to the cell body. Blockade of protein synthesis has been shown to inhibit learning and memory, demonstrating a direct functional link between dendritic protein synthesis, synaptic remodeling, and behavior. Recently, we made the exciting discovery that O-GlcNAc glycosylation is required for activity-dependent protein synthesis in dendrites. Here, we will investigate this discovery in greater mechanistic detail to understand how O-GlcNAc glycosylation regulates dendritic protein synthesis and its consequences for synaptic plasticity. In addition, we will probe whether elimination of O-GlcNAc glycosylation in the brain leads to learning and memory deficits in mice. A unique feature of this proposal is the seamless integration of chemistry with challenging neurobiological studies. We believe that the combination of cutting-edge chemical tools with state-of- the-art neurobiological approaches will be necessary to address the complex, fundamental question of how memories are stored. The proposed studies will significantly advance our understanding of the structure-activity relationships of carbohydrates in the brain and reveal new insights into the molecular basis of learning and memory. At the same time, our studies may ultimately impact the development of pharmaceuticals by revealing novel molecular targets and processes for the treatment of cognitive deficits associated with aging, brain injury, mental retardation, and neurodegenerative disease. PUBLIC HEALTH RELEVANCE: A major goal of this work is to elucidate molecular mechanisms that underlie neuronal communication and hence form the basis of learning and memory. Through the discovery of novel small molecules, proteins and pathways involved in neural communication and function, this work may aid ultimately in the development of new pharmaceuticals designed to improve cognition deficits associated with aging and neurodegenerative disease.